I mentioned Octal as being base 8. It’s true. However in Linux circles you can either set permissions on a file or folder using user/group/other I always found it clunky. Instead you can just do a chmod 551
It breaks down as follows:
4 is read
2 is write
1 is excute
So chmod 551 says User can read and execute, group can read and execute, and other only gets to execute.
You just add up the values to get the permissions for each. All privs come up to chmod 777, that’s read, write and execute for EVERYONE.
But you can understand why it’s called Octal – only 8 possible values for each position.